Solar Tilting Logic

[StarDreamers.us]

Great discussion on a very important topic. Thanks!

Another question: In the big tent at the Quartzite RV show in January of 2006 there was a fellow there pitching his powered tilting system. He was looking for funding and someone to make the system. Does anyone know what happened to him or his ideas? He had a working system in his booth. It looked good.

 

Safe Travels!

[sushidog]

Today while I was on the road, I saw an older Class A with the back half of the roof (or maybe a little more) covered with what looked like a solar roof rack made of angle aluminum. The rack was just high enough to clear the AC shrouds. This arrangement shaded their roof, making it cooler inside the RV for sure, as well as boosting the panel's efficiency by allowing them to run cooler due to the increased cooling airflow underneath. Assuming the rack was about 24ft long (a close guestimate) it could easily fit 6, 395 watt SUN panels for 2,370 watts, or 6 of the even smaller footprint 435 watt E20 SUNs for 2,610 total watts. Few would need more power than this, but if you did, just make it a little longer. Cost of the panels: as low as 44 cents/watt for the 395 watt panels (in quantities of at least 15) from Sun Electronics http://sunelec.com/solar-panels/high-voltage-solar-panels/sun-395-watt-monocrystalline-solar-panel.html At this low price, why experience all the negatives of tilting?

 

Chip

[Helipilot]

FWIW the easiest way to determine the best angle is look at your map ( Central US from east to west through Oklahoma is 35* Latitude roughly) and tilt your panels to that latitude. This angle will give you good access to the sun's rays at this latitude.

[Yarome]

Wow! This thread really blew up with some excellent questions and "fixes". Nice!

 

I'm not great with names, so bear with me and I'll try to touch on a few points from my limited experience.

 

Someone asked about charge times. It's going to vary, but when I design a system I want enough wattage up top (on a good day) to see my battery bank topped off around lunch time. A quick glance at my soc and I know I have free energy on tap to get the laundry done, recharge laptop batteries, etc. Running your genset in the morning is another strategy. It will handle some big loads and get your bb up to 90% in a heart beat, then let your panels handle the rest. Personally, I'm pretty low tech. I use a hand grinder and french press for my coffee so I leave the grunt work to my panels and have very modest energy usage. This time of year my batteries have been topping off around 11am so I have more juice than I know what to do with.

 

Again, the all important is to size your battery bank and panels to fit your particular life style. Using a half day as a general rule of thumb on a recharge cycle will generally suffice.

 

Tilting. I think that's been beaten to death already. With my build, I like being tilt capable, but in practice, I've only used it for cleaning rather than increasing energy production. Depending on where you like to vacation, I can see where it might be adventageous. My mounts have a single stainless steel screw and dicor. I haven't really considered wind shear. Evidently, for some it has been an issue, but I've never run across anyone that has lost a panel to sustained winds. That is just from my own experiece with the caveat that I am a bit of a goldilocker. I listen to NOAA religiously every morning and get the heck out of dodge if the weather isn't going to be playing nice.

 

Snow. While I make all reasonable efforts to avoid it, I have been caught with my pants down a time or two. In which case I have a tarp with weighted lines. I'm able to toss the lines over my rig, pull the tarp up, and anchor the lines. In the morning it's just a matter of sloughing off the tarp and taking the snow with it.

 

And for John, if you wake up in the middle of the night to a fat man dinking with your exterior 110vac outlet... remember you said I could. :lol:

[Yarome]

 

I don't know if the voltage stays the same and only the amperage goes up as a panel catches more sun.

 

My initial installation will give me 1060 rated watts of panels. It will be charging a 9kwh lithium battery pack holding about 500 usable amps at 12v. Unless I add a second battery pack, the “low hole in my bucket” at this time may be my battery capacity. The lithium battery pack's rated maximum charge rate is 4500 watts, so that should accommodate any amount of solar energy I can capture with these panels and any I add later. I am not sure that my Midnight Solar 150 Classic charge controller will handle all the power my panels can produce at peak, but I expect it should. Maybe someone can tell me more about that too?I H

 

Talk about battery envy.

 

So as you suspected, your voltage will stay about the same, but your amperage will increase as your panels are able to catch more sun. But it's the voltage that is going to be "pushing" amps into your cells, so (not knowing your roof layout) I would try to capitalize on your voltage heading down stream and up that as much as possible. If it's possible, I would be trying to run series arrays and upping voltage to feed your controller. I have no doubt that a midnight solar 150 would be able to handle your daily input, but that's really an expensive option IMO. I would rather go with paralleing a couple of tristar's into my battery bank.

 

My experience with LFP's is EXTREMELY limited though and the above should be taken with a grain of salt. The principles with regard to your panels is sound, but hopefully Techno or Jack will chime in on the back end with regard to your battery bank.

 

It sounds like you have your head about you and are spot on the right track.

[lappir]

Excellent topic, posting on it to have it in my content mostly but will share a few of my hair-brained ideas just for fun. Driving the last couple days from Florida to Iowa I noticed a field of Sunflowers and all the flowers were facing the same way. I'm sure those of you who have driven through Kansas have noticed this too. What makes the plants do this? I'm sure if I Google it or use Wikipedia the real answer will be there but let me just use my "common sense" from my experience. I say it's a capillary action of the fluid in the plant. The heat of the sun expands the fluid on one side causing the tilting of the flower head. In my memory I think the flowers face away from the sun. Now what does this mean in a Solar topic? Well my idea is to have a center mount for the panels with a 360 degree hydraulic system that would keep the panels tilted toward the sun no matter where it was in comparison the the North South or East West position of the vehicle they were mounted to. It would probably be a plumbing nightmare but the fluid in the system could be used to provide a heat source for the water heater.

 

Like I said just posting to keep in my content. Hope some got a laugh.

 

Rod

[oldjohnt]

Yo sushidog,

 

I LIKE that 395 Watt Panel you linked. If I were starting all over from scratch I would soooooooooooooo buy that panels as its much cheaper then the four 100 Watt Panels I currently have. I may have to go on top the RV today and take some measurements lol My current MPPT Solar Charge Controller is rated for 150 volts which could handle the panel you linked. I agree, why mess with tilting if you have available the real estate for panels such as that which meets your energy requirements...

 

Yarome,

 

Sure I said you can hook to my 110 outlet, but its fused at ONE amp !!!!!!!!!! don't use all that up the first try now lol

 

1 Rod,

 

Hey they have RV rooftop Satellite Dish Receivers that lock on and follow the satellite, why not follow the sun ??? The engineering and logistics to lock on and follow that big bright light and energy source in the sky isn't very complex, but the mounts, hinges, drives and actuators for 360, now that gest a bit sticky and expensive I'm sure

 

John T

[Yarome]

Sure I said you can hook to my 110 outlet, but its fused at ONE amp !!!!!!!!!! don't use all that up the first try now lol

 

 

Fine. No coffee for you!

 

That's just too funny. You might be surprised what I can do with a free amp on tap.

[reed and elaine]

This has been a fun thread and have read all the posts and enjoyed them.

 

Bill - agree with concept of putting extra panels on ground mounts. Have seen articles on this and noticed on the Technomadia and perhaps Gone with the Wynns or Wheelingit that they use additional panels to track the sun. Insolation is Lambertian so that energy deposit goes as cosine e.g. 45 degrees means you get .707 of normal.

 

Rif – I guess that from your admission of tilting that you are now a charter member of PTA (panel tilters anonymous).

 

Cathy and Jim - As others have noted (Yarome below), going to higher voltage means lower amperage at the same wattage. Have photo of brushing off snow from ladder(page 1 of this thread) but prefer the idea that Yarome noted of tossing tarp over the panels before it snows and pulling it off with snow afterwards. Unfortunately, our experience is that it starts snowing about 2 in the morning and its snow surprise in the morning.

 

Agree with Yarome on utilizing higher voltage (see comment above). Our son designed system as Yarome suggests: two series of 3 x 235 W (30 V each) = 90 V for each series. These two series are then parallel to controller. We have drawn over 1400 W to our TriStar MPPT-45 at 90 V. This is only 14 amps at 90 V. It would be 116 amps at 12 V.

 

Reed and Elaine

[StarDreamers.us]

Information please? Has anyone used the 395 watt panel? I would be interested in some user information. It is so much bigger than my current Sharp 200 w panels. Thanks for sharing. Having to buy 15 panels, could be a problem. What about the technology of the panel. Thanks so much for sharing.

 

Safe Travels!

[reed and elaine]

StarDrreams us

 

You must have a really large rig for 3 kW of panels. You could run two air conditioners

 

Googled that Sun 395 W panel

Dimensions: L: 92.4in x W: 48in x H: 0.4in
Weight: 75.00lb

• Peak Power (Pmax) 395 Wp
• Maximum Power Point Voltage (Vmpp) 82 V
• Maximum Power Point Current (Impp) 4.79 A
• Open Circuit Voltage (Voc) 105 V
• Short Circuit Current (Isc) 5.33 A
• Cells per Module: 160
• Solar Cells: Monocrystalline Silicon
• Cell Dimension: 125 mm x 125 mm

 

Just cut a piece of cardboard the same size as the panel (template) and move it around the roof of your rig to see where they can fit without shadowing. Sounds as if you would use seven panels. With that voltage you would probably run them in parallel since 560 Vmp for series would be a bit much.

 

Four feet wide is fairly wide and you would only have 6" between the panels on the roof if you ran them parallel along the roof sides. Should be no problem with the 92" LENGTH

 

IRod - let us know how your SunFlowrconcepts works out.

 

Reed andElaine

[Yarome]

StarDreamers - I don't know if I would feel too comfortable going with a 395watt panel on an RV roof mount. That's a LOT of real estate and you would have to be pretty clever about how to keep something that size attached.

 

Reed and Elaine - You do realize that whole 2am snow thing only happens to people with more than a grand of panels up top. If you were to take a few panels down that wouldn't happen. I was kind of surprised you're pumping all that juice through a 45 rather than a 60amp controller, but then again, I don't have any practical experience with LFP systems. Is there an advantage to using the lower output?

 

Rif - It seems like I haven't heard from you much lately, but now that we know you've been stuggling with PTA it makes a lot more sense. Keep up the good fight, brother. Were here for you.

[Yarome]

Googled that Sun 395 W panel

Dimensions: L: 92.4in x W: 48in x H: 0.4in

Weight: 75.00lb

• Peak Power (Pmax) 395 Wp
• Maximum Power Point Voltage (Vmpp) 82 V
• Maximum Power Point Current (Impp) 4.79 A
• Open Circuit Voltage (Voc) 105 V
• Short Circuit Current (Isc) 5.33 A
• Cells per Module: 160
• Solar Cells: Monocrystalline Silicon
• Cell Dimension: 125 mm x 125 mm

 

Wow! Those are no joke. Starting your own city are ya?

 

No suggestions over what Reed said, I just had to comment. LOL

[Keelandb]

OK, I'm in the process of installing solar panels on my Class C. Unfortunately it is a very long process for me. I do plan on having the option of tilting them. I may or may not actually tilt them, depending on situations that may come up.

 

My question is about having the panels flat mounted. How flat do you mean? A slight tilt allows rain to run off and, hopefully, wash away any debris. With my home mounted panels that are tilted at about 45 degrees I still need to occasionally wash the panels to remove the pollen/leaves/etc. On an RV how flat should flat panels be mounted to allow some 'washing' by the rain? Or do you recommend "getting on the roof" to clean them occasionally?

 

On the RV I have four 158W panels from DMSolar that will be run in two pairs of two in series. That will be about 24 volts (18.9V VMP each panel) down to a Tristar-MPPT-60 and two giant Lifeline GPL-8DL 12 volt AGM batteries (255 amphours each).

[Yarome]

Mine lay perfectly flat. Moving down the road keeps them blown off or I'll shoot some air over them from time to time. I don't go up top, but I'll run the ladder around my rig and hit them with the long scrubber/squeegee once in a while. Just a light dust over them doesn't affect production all that much.

[StarDreamers.us]

Sorry for the confusion on my post about the number of panels needed. I can only use 3-4 panels. The information that I had found indicated lots of 15 panels is how they are sold. Perhaps I read it wrong. Anyone know anything about the type of panels? Has anyone used them? Thanks.

 

Safe Travels!

[reed and elaine]

The Sun site noted that they were sold in lots of 15 but it should be possible to buy four of them from some solar sales site.

[oldjohnt]

Keeland,

 

Its my pure "opinion" for a so called "flat mount" the panels should be tilted very slightly so towards the coaches rear end the panel is just a bit higher then the front end, so when driving down the road the wind exerts a slight down pressure versus lifting. NOTE aerodynamics is all Greek to me lol so no warranty but it seems intuitive if the rear is slightly elevated while driving that's better then if the front were higher???????????? But maybe I'm wrong, its happened before lol

 

I'm sure flat will get you by fine and others have found such NEVER BE A PROBLEM and will swear to it and wouldn't have it any other way and that's all fine and dandy with me. Maybe someone with aerodynamics expertise can shed some light on this???

 

I'm NOT talking much tilt to the rear only slight mind you, it don't take much, plus if parked level the rain will drain off better.

 

I'm NOT going into your tilt methods and mechanics here, only talkin about how flat is flat lol

 

For now at least, that's my story and Ima stickin to it.

 

John T

[Darryl&Rita]

I've seen panel manufacturers spec a minimum 5* slope to avoid water pooling on the panel, & dirty water drying. Don't remember which manufacturer, but mine have all been mounted that way, with no complaints.

[Jack Mayer]

I try to slope the panels to drain water. It does not have to be much - a couple of degrees. It really helps keep them clean.

[skp51443]

My old install was pretty basic, nothing fancy just a drill and jigsaw to make them but they were rock solid, easy to tilt (remove two bolts and add the tilt rods) and it got the panels up off the roof so they ran a bit cooler.

 

 

With your roof you may not need as much anchor area as I had here, going with a sturdy top rail and just short mounting sections will probably be good enough. The short mounting sections are also more friendly to a curved roof.

 

Another gain from bumping up a few inches is that plumbing vents are no longer an issue as the panel happily sits above them.

[Keelandb]

My home built mounts using angle aluminum will have the solar panels about 3 inches above the roof. That is not enough to be above any vents, whether plumbing or air vents. I think that I will elevate the rear of the panel just a bit for both drainage and to provide a bit of pressure to 'keep the panels pressed toward the roof'. Thanks to Daryl&Rita and Jack for the suggestion. I was thinking of a slight slope from side to side, but from front to back makes more sense.

[oldjohnt]

Keeland, to your statement

 

"I think that I will elevate the rear of the panel just a bit for both drainage and to provide a bit of pressure to 'keep the panels pressed toward the roof'. Thanks to Daryl&Rita and Jack for the suggestion. I was thinking of a slight slope from side to side, but from front to back makes more sense."

 

FWIW I say DITTO and I agree 100%

 

Take care now

 

John T

[Jack Mayer]

I think you will find that at most mounting heights having the back slightly raised really is not exerting any significant down pressure on the panels. I've not put load cells or anything exotic on them to measure it...but I HAVE left some loose masking tape stuck to the edge of the panels, and I HAVE left "loose" wire ties ON the panels and after 500 miles of driving they were still there.

[oldjohnt]

That's right Jack and the more raised the more force the winds exerts. I never measured any angles but it was just intuitive as I mentioned above the back should be at a slight higher level then the front (also drains better) which would exert at least some albeit small downward force. I cant imagine mounting them otherwise with the front HIGHER then the back????

 

Since we all agree this must be right lol

 

Safe travels yall

 

John T